The present invention relates generally to circuitry for providing a regulated voltage output and more particularly to such circuitry which responds rapidly to sustain the power requirements of a load, while maintaining high efficiency to render the implementation thereof compact in both size and weight.
DC power supply circuitry for directing current to a load at a constant voltage is well known in the electrical arts. As explained in an article entitled POWER SUPPLIES which was published by Power-One, Inc. on pages 160 and 163 in the May 1989 edition of EVALUATION ENGINEERING, linear and switching regulators are the most fundamental forms of such circuitry. The advantages of linear regulators are very low noise and excellent regulation in regard to both line (voltage) and load (current), while the advantages of switching regulators are high efficiency and a very compact nature in regard to both size and weight. For a linear regulator, the advantages are derived from its continuous operation, and for a switching regulator the advantages are derived from its periodic operation. Disadvantages are also inherent to each type of regulator, with greater thermal dissipation causing lower efficiency to result from the continuous operation of linear regulators, while switching noise and slower response result from the periodic operation of switching regulators. For comparable power output therefore, linear regulators are preferred for their electrical operating characteristics but they are much larger in size due to heat sinks for much greater thermal dissipation, while switching regulators are preferred for their much smaller size and weight but their electrical operating characteristics present problems.
Circuitry combining linear and switching (or chopper) regulators for particular applications is well known in the art.
One such combination is found in U.S. Pat. No. 3,600,667 wherein the linear and switching regulators are interconnected with the output of the former being fed back to control the power output time duration of the latter. Another such combination is found in U.S. Pat. No. 4,502,152 wherein the linear and switching regulators operate independently with only their outputs connected in parallel to supply a power output. However, the linear regulator has the higher voltage output and therefore, it alone supplies ripple free power under predefined steady state load conditions, while only the switching regulator supplies power under predefined transient load conditions which result when power demand is increased. Consequently, the power supply concept of this patent is exactly opposite to that of the invention disclosed and claimed herein, as will be clearly understood from the disclosure provided hereinafter.